Efficient detection of 45 ppb ammonia at room temperature using Ni-doped CeO₂ octahedral nanostructures

To meet the requirements in air quality monitors for the public and industrial safety, sensors are required that can selectively detect the concentration of gaseous pollutants down to the parts per million (ppm) and ppb (parts per billion) levels. Herein, we report a remarkable NH₃ sensor using Ni-doped CeO₂ octahedral nanostructure which efficiently detects NH₃ as low as 45 ppb at room temperature. The Ni-doped CeO₂ sensor exhibits the maximum response of 42 towards 225 ppm NH₃, which is ten-fold higher than pure CeO₂. The improved sensing performance is caused by the enhancement of oxygen vacancy, bandgap narrowing, and redox property of CeO₂ caused by Ni doping. Density functional theory confirms that O vacancy with Ni at Ce site (V_ONi_Ce) augments the sensing capabilities. The Bader charge analysis predicts the amount of charge transfer (0.04 e) between the Ni-CeO₂ surface and the NH₃ molecule. As well, the high negative adsorption energy (≈750 meV) and lowest distance (1.40 Å) of the NH₃ molecule from the sensor surface lowers the detection limit. The present work enlightens the fabrication of sensing elements through defect engineering for ultra-trace detection of NH₃ to be useful further in the field of sensor applications.